The technology of fabricating Infrared (IR) sensitive silicide Schottky barrier detectors has progressed gradually over the past fourteen years. The first low-barrier-height detectors were made using palladium silicide (Pd.sub.2 Si) Schottky diodes having a barrier-height of 0.35 eV, corresponding to a detector cutoff wavelength of about 3.5 microns [F. Shepherd, A. Yang, IEDM Tech. Dig., pp. 310-313 (1973)]. The next major breakthrough in low-barrier silicide technology came with the discovery of platinum silicide (PtSi) detectors, which have a barrier height of 0.22 eV, corresponding to a cutoff wavelength of about 5.6 microns [B. Capone et al., 22nd International Technical Sym. SPIE, San Diego, p. 120 (August 1978)]. The PtSi Schottky-barrier detector has evolved to become a mature technology and large-size imaging arrays ontaining more than 250,000 detector elements have been demonstrated using this technology.
There is a strong interest in extending the spectral response of Schottky IR detector further into the long wavelength band from 8 to 12 microns. Experiments have demonstrated [P. Pellegrini, et al. IEDM Tech. Dig., pp. 157-159 (1982)] that iridium silicide has the lowest barrier height on p-type silicon of any known metal. (See, also, U.S. Pat. No. 4,533,933 to Pellegrini et al. for a description of a Schottky barrier diode formed of iridium-silicon material.) Barrier-heights of 0.125-0.152 eV have been measured in iridium-silicide detectors corresponding to a cutoff wavelengths of 8-10 microns. However, detectors fabricated with Ir silicides generally have low quantum efficiencies and irreproducible characteristics. Comparison of reaction kinetics between Pt and Ir metals with silicon indicates that Pt is the dominant diffusion species in the formation of Pt silicide, whereas Si is the dominant diffusion species in the formation of Ir silicide. As a result, Ir silicide formation requires higher temperatures than Pt silicide and exhibits less reproducible characteristics. The presence of interfacial impurities also reduces the efficiency of internal photoemission and, therefore, reduces detector quantum efficiency. Aside from these disadvantages for Ir silicide, fabrication of Ir silicide detectors is also more difficult than that of Pt silicide.
The fabrication procedure for Pt silicide diodes is well established and is outlined in the prior art drawings of FIGS. 1(a)-1(e).
In the first step of the prior art process for the formation of platinum silicide diodes, as shown in FIG. 1(a), an n-type guard ring structure 14 is formed in a p-type silicon substrate 10 in the well-known manner, using n-type dopants, such as phosphorus. Next, an SiO.sub.2 oxide layer 12 is formed over the guard ring structure and substrate 14 and 10, respectively, such as by the well-known oxidation or vapor deposition processes.
Next, as shown in FIG. 1(b), a suitable mask (not shown) is placed over the SiO.sub.2 film 12 and an opening 16 is etched in the SiO.sub.2. This opening extends to about the middle diameter of the n-type guard ring 14 to provide access for the subsequent silicide contact formed on the radially inner edge of the guard ring.
Next, as shown in FIG. 1(c), a thin film of platinum 18 is deposited utilizing, for example, an electron-beam deposition process. The platinum film 18 is deposited over the entire top surface, covering both the SiO.sub.2, a radially inner portion of the guard ring 14, and a portion of the silicon substrate 10 beneath the previous opening 16.
Next, as shown in FIG. 1(d), the device is subjected to heat treatment to form a platinum silicide disc-like portion 20 in the SiO.sub.2 opening.
Next, the device is wet etched in aqua regia to remove the unreacted platinum 18 on the SiO.sub.2 layer 12, as shown in FIG. 1(e).
The above described process is a self-aligned process which has proven to be extremely reproducible and is the key to the successful development of large-size Pt silicide detector arrays. However, the self-aligned process is not adaptable for iridium silicide devices. Iridium is only slightly soluble in aqua regia and reaction of iridium with SiO.sub.2 further prevents the removal of iridium. Accordingly, there is a need for the development of a new fabrication procedure for the manufacturing of iridium silicide detector arrays. Furthermore, the new procedure should improve the reproducibility of the silicide formation and increase the quantum efficiency of the silicide detector.